1. Technical Field
The present invention relates to a controller of a graphic equalizer using multiple control devices for specifying levels of multiple frequency bands.
2. Related Art
A graphic equalizer is a kind of tone controller that uses multiple control devices for specifying levels of multiple frequency bands (hereafter referred to simply as bands). Just looking at each control device's position can identify the corresponding frequency characteristic.
The following describes an example of using fader control devices as control devices assuming j to be 31, where 31 is the total number of bands and control devices, respectively.
FIGS. 9(a) through 9(d) are an explanatory diagram showing a conventional graphic equalizer. The following describes a case where a display device displays multiple fader control devices as symbolic images of GUI and a mouse tool is used to manipulate each fader control device through GUI.
FIGS. 9(a) and 9(b) are explanatory diagram showing operation panel display screens.
Reference numeral 11 denotes an operation panel display screen; 12 denotes a display portion for graphic equalizer numbers; 13 denotes a reference line to indicate a reference level (neutral level 0 normally equivalent to 0 db); and 141 through 1431 denote fader control devices corresponding to bands 1 through 31.
In FIG. 9(b), the mouse may be used to move the pointer 15 to fader control device 145. Pressing a mouse button selects fader control device 145. Its outline is displayed in a thick, red line to indicate that the fader control device is focused. Dragging the mouse vertically moves fader control device 145. The level corresponds to the operated position after moving the fader control device. This level is assigned to a band No. 5 corresponding to fader control device 145.
FIG. 9(c) is a block diagram showing graphic equalizer GEQ1 using as many digital filters as the total number of bands j.
Generally, graphic equalizer GEQ1 is implemented by serially connecting digital filters 211 through 2131. The total transfer function of GEQ1 results from multiplying respective transfer functions of digital filters 211 through 2131.
The digital filters 211 through 2131 are permanently assigned to bands 1 through 31 in order. Each digital filter functions as a peaking filter that increases or decreases level G for the corresponding band from the reference level (i.e., neutral 0 db).
FIG. 9(d) is a block diagram exemplifying the inside configuration of each digital filter. For example, the digital filter is composed of an IIR (Infinite Impulse Response) filter. In FIG. 9(d), reference numerals 101, 102, 107, and 108 denote delay means with the transfer function set to z−1; 103, 104, 105, 109, and 110 denote coefficient multiplier; and 106 denotes an adder.
Fader control devices 141 through 1431 are used to specify levels for the respective bands. A coefficient value table is provided for each band. In accordance with the level specified for each band, referencing the coefficient value table obtains parameter values (coefficient values) to be set to the coefficient multipliers 103, 104, 105, and 109 to the control digital filters 211 through 2131 assigned to the bands.
Selectivity Q is configured to increase as level G is set to be smaller or greater than the reference level. By contrast, selectivity Q is configured to decrease as level G is set to approximate to the reference level. In this manner, control is provided to maintain the bandwidth even though level G changes.
The digital mixer described in non patent document 1 uses a DSP (Digital Signal Processor) and is capable of individually inserting up to 24 numbers of 31-band graphic equalizers GEQs into any input or output channels.
When the DSP is used to implement the graphic equalizer GEQ having multiple digital filters, there is a limitation on the DSP throughput.
The graphic equalizer GEQ is not always used to manipulate all bands. When the graphic equalizer GEQ is inserted to suppress howling of a sound picked up through a microphone, for example, the graphic equalizer GEQ is operated for only a part of the multiple bands. In such case, however, the DSP must process signals of all the digital filters, causing a problem of loading the DSP with unnecessary processes.    [Non patent document 1] CS1D Reference Manual (Software) ver. 1.41, YAMAHA CORPORATION. See also pages 13 to 16 on the Internet online manual http://www2.yamaha.co.jp/manual/pdf/pa/english/mixers/CS1DE.pdf.